When comparing SourceTree vs GitKraken, the Slant community recommends GitKraken for most people. In the question“What are the best Git clients for Windows?”GitKraken is ranked 2nd while SourceTree is ranked 3rd. The most important reason people chose GitKraken is:

It's modern and beautiful, it looks clean and refined.
It's simple: the most used features (pull, push, branch, stash, commit) are accessible in one click, and are the only buttons. The other features aren't in complicated menus nor in hundreds of buttons, but rather displayed when you right-click on something.
It gives more space to the commits, i.e. the most important things. In fact, you can collapse or reduce the other menus/windows.
It displays the current path (project, branch) on an horizontal (clickable) bar at the top. It's just a matter of taste but I prefer this to the traditional "tree" view.
It has undo and redo buttons on the main window.
It supports some drag-and-drop gestures (for example: drag-and-droping the local branch to the remote one pushes it).

Comprehensive layout

History view tracks changes made to the currently selected repository. It's divided into three sections. The top section has a graph with progression of commits, branches, and merges. The bottom section shows commit details, files changed, and differences committed.

There's also a toolbar at the top that allows switching between the three views, as well as giving access to git commands (such as commit, checkout, reset, stash, add, remove, fetch, pull, push, branch, merge, and tag).

Pro

Built-in integration with Stash and Bitbucket

Pro

Quick setup

Once installed, SourceTree will automatically try to look for and set up repos that are worked on. SourceTree will also detect if git-flow is used and what is the current development state as long as default git-flow branch names are used.

The software tracks all relevant repositories in the bookmark's window. Repositories can be added to the list by creating new ones, adding a local folder, supplying a clone URL or integrating with remote services such as Bitbucket or GitHub.

Pro

Supports Git, Mercurial, and Subversion

Allows managing Git & Mercurial repos side by side. It even allows Subversion interoperability via git-svn or hgsubversion plugins which set up a bridge between either Git and SVN or Mercurial and SVN respectively.

Pro

Allows chunks and lines selection during commit

SourceTree automatically splits the changes to be committed into chunks allowing committing (or discarding) each chunk separately. Furthermore, the user can even select specific lines. This greatly increases the flexibility of the user in that matter.

Pro

Built-in Git-flow and Hg-flow support

Git-flow and Hg-flow provide a consistent development process by defining a strict branching model that is great for managing large projects.

SourceTree allows setting up and integrating into repos that follow this model. Clicking the Git-flow / Hg-flow toolbar button will give you access to actions for starting or finishing features, releases or hotfixes depending on the current state of repository.

Pro

git terminal

Comes with own built-in git termnal independant from other git installations and updated regulary. It's especialy good for git beginners who would like to use advanced git functions, but are not ready yet.

Pro

Supports Git LFS

Pro

Beautiful user interface

It's modern and beautiful, it looks clean and refined.

It's simple: the most used features (pull, push, branch, stash, commit) are accessible in one click, and are the only buttons. The other features aren't in complicated menus nor in hundreds of buttons, but rather displayed when you right-click on something.

It gives more space to the commits, i.e. the most important things. In fact, you can collapse or reduce the other menus/windows.

It displays the current path (project, branch) on an horizontal (clickable) bar at the top. It's just a matter of taste but I prefer this to the traditional "tree" view.

It has undo and redo buttons on the main window.

It supports some drag-and-drop gestures (for example: drag-and-droping the local branch to the remote one pushes it).

Pro

Cross-platform

Built on top of Electron, so it runs on Linux, Mac, and Windows.

Pro

Free version available

There are both pro and free versions available. The free version is pretty complete feature-wise for day-to-day operations.

Pro

Extremely easy to use

A lot of care has gone into trying to make GitKraken as easy and intuitive as possible and it show. Every action is quick and painless with no more user interaction than necessary. For example, switching to another branch is as easy as a double-click on the sidebar.

Pro

Offers a simple way of undoing mistakes

GitKraken has simple undo/redo buttons that work the same way you'd expect in any other software.

Pro

Some of the best integration with hosted version control services

GitKraken can be connected to Github, Gitlab, or Bitbucket accounts through OAuth. From that point onward most if not all actions that are related to these services can be done inside GitKraken. Things like: cloning or forking a repository, adding a remote, pushing to a remote repository hosted on these services can be done inside the app.

You can even manage pull requests inside GitKraken for example. All pull requests for a certain branch for example are shown on that branch's graph.

Pro

Under constant improvement

A quick glance at GitKraken's release notes shows how frequently it's updated. Updates are released on a 2-4 week cycle and each one brings new features and bug fixes.

Pro

GitFlow support out of the box

Supports GitFlow out of the box.

Pro

Has a FuzzyFinder

GitKraken has a fuzzy finder to switch between repos / files.

Pro

Good keyboard shortcuts

Pro

Perfect for beginner developers

GitKraken is easy to use and is brilliant for the beginner developers

Cons

Con

Requires an account to install and use

Need an Atlassian account to install.

Con

Can sometimes be slow

Some operations can be slow. If you know what you want (e.g you want to touch a file, add it, commit it, and push it) you can do it much faster on the command line. However you're often not going to know what you want, so the visual diffs (for example) help massively.

Con

Does not allow offline installation

Upon installation, the splash screen prompts you to login. There used to be a workaround for you to manually deploy this application in an offline environment, but they've patched it as of 2.0.20.1. It now does a dial-home on each start-up. Since it cannot reach the server, it throws an error to the user, and raises alerts to compliance.

Atlassian's final decision was that they are not going to support this feature at all. Quoted from their staff:"We’ve never officially supported any form of pre-installation on device management capabilities. [...] As you know, last year, we removed the notion licensing and asked our developers to register the product by creating an Atlassian account. That said, SourceTree has always been a tool for the individual (emphasis mine) developer."

Con

Not even possible to change the password

There are tickets about this issue sitting there for years and marked as medium priority. I experienced this since version 1.8. Up until now, there has been no fix. If your company's policy is going to enforce you to change your password, it means you need to remove all the repos and clone them again everytime you change the password. This is the worst ever experience.

Con

Unstable and terrible UX

The Windows version of SourceTree is riddled with bugs, causing some users to find it unusable.

These include failing to refresh, frequent freezing, and slow performance. The recent redesign (February 2016) has made the UI difficult to navigate.

Con

Information density can be a bit much

It's possible to become overwhelmed with the information density presented in SourceTree. This is especially the case in history view, as it includes a lot of data presented in various ways.

Though this is great for getting a comprehensive overview of everything that's happening in one place, it can take some getting used to.

Con

Varied speeds across different versions

For example, the Windows version is quite slow is comparison to the Mac version.

Con

"Always-Online" Requirement

As of 2.0.20.1, it needs to dial home on every start-up, else it raises alerts to compliance.

Con

Chews CPU

Con

Browsing folders is troublesome

Choosing files of specific folders for check-in is troublesome.

Con

Not always recognizes changed files

Seems to not always recognize changed files, which means that they will not be pushed to remote origin either. This means if you switch branches, the files will be overwritten and you lose your progress. Very annoying.

Con

Always slow

Con

No dark theme

Con

The UI of version 2.0+ is so terrible

Tab looks good if you have no more than five repos. If you have a lot, you will know my pain. The source tree will not remember the order of the tab you drag. Everytime you restart the app, it will go back to whatever it likes.

Con

Blame MS Office's word correction dictionary to be the source of the slowness while it's not.

It's so obvious that ever since 2.0, it will try refreshing each of the repo a few minutes. If you have a lot then it will drive you crazy. When you try to expand a branch node, it refreshes. Try again, OOPS, it refreshed again. Sometimes, it will take you five minutes to select the node you want.

Con

Has trouble with Github's Yubikey integration

When your 2FA is a hardware key, it is difficult to find a way to bring up the ability to use anything but a pre-programmed password function on the Yubikey, which doesn't add much to security all things considered what a hardware key is supposed to do.

Con

Has memory-related issues

Like most Electron apps, GitKraken has some memory-related issues. For starter, it requires more memory for an action than an equivalent non-Electron application. Although this should not be a problem most of the time for people who use machines with lots of RAM (after all, RAM is pretty cheap nowadays), it can have some issues when opening large repositories and there have been cases where GitKraken failed to open very large repositories or started lagging once they were opened.

Con

Must log into GitKraken servers to use the free version

All functionality is disabled unless you register for a free account and remain logged in.

There is the $79/user/yr Enterprise option. It allows you to deploy a Linux License Server in an air-gapped/offline environment.

Con

Not open source

It is gratis (no cost) but is not open source. The community cannot fix problems in it, audit it for security, or trust it in general.

Con

Crashes once in a while

Under specific circumstances, like resetting 5000+ changes, the GUI will crash.

Con

Not free for commercial use

The free version of GitKraken cannot be used in commercial projects.

Con

Amending merge output is a pro feature

In most cases of Merge Conflicts, users are stuck with auto-merge or manually resolving it by hand. This is because in the Free Tier, users can only (1) Keep File (ver 1), (2) Keep File (ver 2), (3) Auto-merge, or (4) Use External Merge Tool.

In addition, using External Merge Tools is very limited because GitKraken (all tiers) restricts External Merge Tools to only those it managed to Auto-detect. It also does not support custom arguments for the External Tools.

Modifying the merge output directly, or Selecting lines to keep/discard, is a Paid Feature.

Con

Cannot multi-select files

No Ctrl-Click or Shift-Click for multi-selecting files. For example, if you have a few files you wish to delete, it is a slow process. You have to delete them individually; that is, right click a file then delete, right click another then delete, and so on.

Con

Slow

Can take between 2 and 5 seconds to load a repository, if not crashing while loading